This invention generally relates to thermal inkjet printing. More particularly, this invention relates to the apparatus and process of manufacturing precise polymer orifices comprising epoxy, polyimide or other negative acting photoresist material using direct imaging techniques.
Thermal inkjet printers typically have a printhead mounted on a carriage that traverses back and forth across the width of the paper or other medium feeding through the printer. The printhead includes an array of orifices (also called nozzles) which face the paper. Ink (or another fluid) filled channels feed the orifices with ink from a reservoir ink source. Applied individually to addressable energy dissipation elements (such as resistors), energy heats the ink within the orifices causing the ink to bubble and thus expel ink out of the orifice toward the paper. Those skilled in the art will appreciate that other methods of transferring energy to the ink or fluid exist and still fall within the spirit, scope and principle of the present invention. As the ink is expelled, the bubble collapses and more ink fills the channels from the reservoir, allowing for repetition of the ink expulsion.
Current designs of inkjet printheads have problems in their manufacturing, operating life and accuracy in directing the ink onto the paper. Printheads currently produced comprise an inkfeed slot through a substrate, a barrier interface (The barrier interface channels the ink to the resistor and defines the firing chamber volume. The barrier interface material is a thick, photosensitive material that is laminated onto the substrate, exposed, developed, and cured.), and an orifice plate (The orifice plate is the exit path of the firing chamber that was defined by the barrier interface. The orifice plate is typically electroformed with nickel (Ni) and then coated with gold (Au), palladium (Pd), or other precious metals for corrosion resistance. The thickness of the orifice plate and the orifice opening diameter are controlled to allow repeatable drop ejection when firing.). During manufacturing, aligning the orifice plate to the substrate with barrier interface material requires special precision and special adhesives to attach it. If the orifice plate is warped or if the adhesive does not correctly bond the orifice plate to the barrier interface, poor control of the ink drop trajectory results and the yield or life of the printhead is reduced. If the alignment of the printhead is incorrect or the orifice plate is dimpled (non-uniform in its planarization), the ink will be ejected away from its proper trajectory and the image quality of the printout is reduced. Because the orifice plate is a separate piece in conventionally constructed printheads, the thickness required to prevent warping or buckling during manufacturing requires the height (related to thickness of the orifice plate) of the orifice bore to be higher than necessary for thermal efficiency. Usually, a single orifice plate is attached to a single printhead die on a semiconductor wafer that contains many printheads. It is desirable to have a process that allows for placement of the orifice plates all at once across an entire semiconductor wafer to increase productivity as well as ensure accuracy of orifice placement.
The ink within the firing chamber fills the orifice bore up to the external edges of the orifice plate. Thus, another problem with this increased height of ink in the orifice bore is that it requires more energy to eject the ink. Additonally, high quality photo printing requires higher resolutions and thus smaller drops of ink. Therefore, a need for a thinner orifice plate that is manufacturable exists. Furthermore, as the quantity of ink expelled in each drop becomes smaller, more orifices are required within the printhead to create a given pattern in a single passing of the printhead over the print medium at a fixed print speed. To prevent the printhead from overheating due to the increased number of orifices, the amount of energy used per orifice must be reduced.
Additionally, in the past, the lifetime of the printhead was adequate. The printhead was part of a disposable pen that was replaced after the ink supply ran out. However, user expectations for quality are driving the need to have a low cost, long life printhead with multiyear permanence and the present invention helps fulfill this expectation.